The concentration of dopantintroduced into the host nanoparticle alters its structural, optical and morphological properties. This paper explains the one pot synthesis of zinc doped cadmium selenide nanoparticles (Zn-CdSeNPs) using L-cysteine as capping agent. The synthesis process was carried out with three necked flask at 90°C. The X-ray diffraction (XRD) pattern confirms the formation of zinc blende cubic structure. Scherrer equation was used to calculate crystal size, and the results showed that crystal size decreased with an increase in dopant concentration. Pure CdSe nanoparticles had a crystal size of 24.66 nm and 15% Zinc doped CdSe had a crystal size of 17.72nm. Results from photoluminescence (PL) spectroscopy shows that at high concentration of Zn dopant, the emission peak shift to higher wavelength and the intensity of the peak decreased. 1% zinc doped CdSe nanoparticles had the highest intensity while 15% Zn-CdSe nanoparticles had the lowest PL intensity.The optical properties of Zn-CdSeNPs were characterized with Ultra Violet visible spectroscopy. Tauc’s plot was used to obtain the bandgap energies of nanoparticles. The results showed that at 11% Zn-CdSe the bandgap energy was 1.35 eV and at lower dopant concentration 1% the bandgap energy was 1.92 eV.